Energy-converting electrical instrument



Mayl2, 1925. 6 1,537,671" v C. W. HEWLETT V I ENERGY CONVERTING ELECTRICAL INSTRUMENT Filed Sept. 9, 1920 2 Sheets-Sheet l H'HHHFH- Q MM . 1,537,671 c. w. HEWLETT ENERGY CONVERTING ELECTRICAL INSTRUMENT Filed Sept. 9, 1920 2 Sheets-Sheet 2 Patented May 12, 1925.

-UNITE D STATES CLARENCE. WIL ON HEWLETT, or IOWA CITY, IowA, AssIeNoR, BY DIRECT AND MESNE ASSIGNMENTS, To GENERAL ELECTRIC COMPANY.

ENEReY-ooNvEnTI e ELEo'TRIcAI. INSTRUMENT.

- Application filed September 1 To all whom it may concern: 3

Be it known that I, CLARENCE W. LETT, a citizen of the UnitedStates, residmg at Iowa City, in the county of Johnson and State of Iowa, have inventedn'ew and useful Improvements in Energy-Converting Electrical Instruments, of which the following is a specification. My present invention has for its ob ect the provision of a practically advantageous instrument for converting the energy of variable electricc'urrents into the energy of sound waves, and conversely for converting the energy of sound waves into energy of electrical currents.

To the attainment of the foregoing the in.-.

vention consists in the improvement as hereinafter described .and definitely claimed.

In the accompanying drawings, hereby made apart hereof: j

Figure 1 is a front elevation bodiment of my invention.

of one emthrough the annular. portion thereof. Figure 2-- is a'diagramma-tic View hereinafter explicitly referred to.

Figure 2 is aL/diagram of the noilconnections.

Figure 3 isa perspective of a modification. 7

Figure 4 is a detail diametrical section ofa portion of the same. Similar numeralsof reference corresponding'parts in Figures 1 and 2 to -which reference will first be made.

In addition to supporting means including a base I and an uprightQ, preferably of hard wood, the instrument shown '1Il Figures 1 and 2 comprises fiber annuli 3,

flanged at 4 and exteriorly threaded as shown; interiorly threaded holder annuli 5 and 6 of hard fiber, one of which is equipped. with threaded rods 7 and the other with transverse bores 8 to receive said. rods; nuts 9 on said rods; a diaphragm 10' preferably of aluminum and about .001 of an inch thick, interposed and clamped between the annuli 5 and 6; and pancake coil-members ll-and 19.,fitting snugly in the rings 3. As shown each of the coil-members 11 and 12fcomprises seven annular coils separated by air spaces, respectively wound with No. 22 and 53. gauge copper wire, and having between 90 and 100 turns. The said an-, nularcoils are maintained in spaced rela- Figure 2 is a vertical diametrical section des gnate 9, 1920. Serial No. 409,212[

tion by interposed sections 13 of wood or other appropriate material, and each annular coil is coated with shellac and bound at intervals with linen thread. The successive coils in each set are connected in series, as clearly shown in Figure 2". a

The instrument thus far specifically described is susceptible of use as a transmitter of sound. When so used, a direct current from a battery passes through the coils in series in such a way that the resulting magneticfields in the two sets of coils oppose each other. In the region of the diaphragm the resultant of these two opposing magnetic fields is everywhere perpendicular to,

the axis of the coils; It is evident that the direction of this magnetic field lies along the radii of the diaphragm and hence may be briefly referred to as a radial magnetic field. phragm it. is made to vibrate to and fro.

When sound waves strike the dia-' L This to and fro motion of the diaphragm in A the radial magnetic field generates variable circular electric currents in the diaphragm of the same character as the vibrations'of the diaphragm. These variable currents in the diaphragm induce alternating electromotive I phragm, B the battery for sending direct current through the two coils, and C C are two stopping condensers to afford a path for'the induced electromotiveforces in the two coils to be impressed on the amplifier A. R is a telephone receiver which responds to the amplified current. The direct current passes through one set of the coils from it to 2' and through the other set from i to j. It is to be noted that the induced alte nating electromotive forces are in such directions-that they oppose the direct current in one coil and aid it in the other. I-Ience, at a given instant, the alternating currents come out of the coils at 2' and come into the electromotive forces will "neutralize each other and produce no effect; Manifestly, a transmitter characterizedas'stated 'is free from the many faults common to the carbon granule transmitter;

*At-this point I wouldhavefit construction would be one v in which the annuli holding the coils aremounted ajfiked distance apart, say one thirty second'ofan inch, with the diaphragm supported half wav between them. r V

The. "instrument may also be used" as ,a receiver for" voice' currents. Referring to Figure "2 it is clear that if such variable currents are" sent-intothe instruinent at 71, com'-. ingout at. It and j to 70', these Variable cur-' rents will induce circular currents in the diaphragm .wh1ch will react with the radial magnetic field causing mechanical vibration ofthe diaphragm as is described more in detail in the description of the one coil member embodiment hereinafter described. For use as a head receiver it hasQbeen found preferable to separate the two. coils and mount a separate diaphragm close toeach coil. The two halves of; the instrumeiit may then be placed one half at each'ear. Fo r-.this

purpose each coil of the instrument may be wound of about five thousand turns. of No.

. 40 Band S. gauge enamelledcopper wire.

This makes a coil about 5 inch thick and 2 inches in diameter with a' hole inthecentcr 1 inch in diameter.

It is found that a thicker diaphragm, say inch thick, gives the best results as atr'ansmitt'er of voice currents.

Again the instrument will serve as a. precision source of sound at any desired frequency, and the intensity can easily be varie'dby varying the direct current. At frequenciesof 14000 vibrations per second the sounds can be heard several hundred feet away. The waves from the instrument are nearly plane and such shortwave lengths t'can be concentrated at a point by' means of spherical reflectors. I

It will be further understood that in the instrument described the direct current provides a polarizing field in 'the diaphragm,

' and the diaphragm vibrates with the same frequency as the alternating currents. Said polarizing field is radial in the diaphragm- 1. e., perpendicular to the axis of the coils, and it is this polarizing radial field which reacts with the currents in the diaphragm caused by the alternating current. At this point it is well to state that in the one coilmember embodiment hereinafter described an'dfin which one side ofthe diaphragm is entirely free it is the radial component of the field due to the direct current which is the effective polarizing field.

The instrument of Figures 3 and4 comprisesa' handle 20, holder annuli" 5 and 6 connectedtogether arid to the' handle. 20 as shown, a diaphragmlO clamped between {the 'annuli 5 and 6 and a coil-member 11 arranged at the innerside of the diaunderstood that the adjustable arrangement hereinbefore described 'iszin' no {wise "e'ssential, and that, as a matter,of fachia'better-' phrag'm 10?, and connected with the holder annuliand the handle in the-manner shown onin'anyother manner compatible with the of- Figures 3 and '4- can be connected with valbattery sufiic'ient to give one-half to threefourths of an ampere through the coil memberll. The alternating or'va-riable current will cause the diaphragm 10 to respondwith mechanical vibrations of the same character as that of .the impressed alternating current. A chokfe coil may ;be used to prevent-the alternating current from purpose ofmy invention. This instrument rent produces a magnetic fieldin the dia I phrag'm 10. This may be regarded as made up' of, two 'componentsi. e.,*a"component along the direction of the axis of the coil, and a component along the radii. of the diaphragm. Now when the alternatingv current passes through the coil there is induced I in'the diaphragm circularcurrents whose common axis 1s the collinember 11. These currents react with the radial magnetic field causing to and fro motion of the diaphragm which causes sound .waves to be produced.

The instrument just described is possessed of the following advantages over the ordinary telephone receiver. (1) In case a non- 'magnetic diaphragm for instance aluminum, is used there is no hysteresis loss, and inany case a minimum hysteresis loss'which makes this piece of apparatus particularly useful for high frequency work. (2) A minimum eddy current loss These two advantages make the instrument especially useful for a telephone receiver, in that there is a minimum distortion of acomplex alternating current. This distortion is due to a u a .selective damping of components of difl'erent frequency. The force acting upon the I diaphragm is. also uniformly distributed over its area. These pointsof advantage as sure an unusually faithful reproduction of voice currents. I

An enlarged instrument such as just described can be used for addressing audiences or where any loud speaking instrument is necessary. y

In the form of my invention shown in Figs. 3 and 4, the coil memberll may be wound with No. 1 8 B.- and S. gauge wire and contain about 300 turns; this member may be held in the center through the medium of a .fiber plug 25, threaded into another fiber plug 26 which, in turn, is threaded-into the handle or casing 20. The leads 27 and 28 of the coil member 11 are passed through the plugs and handle or casing as shown.

' It will be apparent from the foregoing that my improvement'elnbodies no iron and hence is not subject to hysteresis loss which especially adapts it for carrying high frequency alternating currents; also, that the improvement embodies a minimum amount ofconducting material and therefore is liable to lose but little energy in the form of hysteresis and eddy current losses which fits it especially for high frequency alternating currents; also, that the improvement is susceptible of use directly as part of or as the whole of the inductance in a tuned resonant circuit. If the improved instrument is used as part of the inductance in the tuned circuit, then the remainder of the inductance in the-circuit may be part of an auto transformer, another tap being .taken off at another point to feed back to the grid of the three-element vacuum tube. In the event of my instrumentbeing used as the whole of the inductancein the tuned circuit then the feed back to the grid may be wound around the outside of the instrument. This using the instrument as the whole of or part of the inductance of the tuned circuit'results in obtaining the maximum efficiency.

It is to be understood in conclusion that i the diaphragm included in my appended claims may in some cases be magnetic al-- though usually for high frequency work it would be desirable to use a non-magnetic. diaphragm.

In Figure 4 the coil is shown as made up of annuli. I desire it distinctly understood however, that I prefer in the actual instrument to employ the coil in compact or solid pancake-coil form.

In the two coil device the coils are divided into annuli to enable sound to pass readily through the coils to the diaphragm when used as a transmitter, and from the diaphragm when used as a receiver or tone generator. By reason of this provision the sound does not-have to pass through a restricted passage as would be the case if the coils were made solid and a more faithful reproduction of the original sound'is thereby obtained. i

A solid coil in the embodiment shown in Figure i is advantageous since by such coil a strong magnetic field can be secured.

Having described my invention, what I claim and desire to secure by Letters Patent '1, ll ad acent netic field produced by the direct current 'in the coil.

2, A telephone instrument comprising a fixedpancake coil and a diaphragm of co ducting material adjacent thereto, said c" being adapted to-carry a constant diret current and a variable current, and said diaphragm being adapted to vibrate solely by reason of the reaction between variable currents induced therein by the variable current in the coiland the magnetic field produced by the direct current in the coil.

3. A telephone instrument comprising a fixed pancake coil and a diaphragm consisting of a sheet of non-magnetic conducting material adjacent and parallel thereto covering substantially the entire area of the coil.

LA-telephone instrument comprising a fixed. pancake coil and a diaphragm of nonmagnetic conducting material adjacent and parallel thereto covering substantially the entire area -of the coil, said coil being adapted to carry a direct current which will hen produce a radial magnetic field in said diaphragm whereby the vibration of said diaphragm in response to sound waves impinging thereon will cause the generation in the diaphragm of variable currents corresponding to the sound waves and the variable currents thns generated will induce corresponding currents 1n the coil.

5. A telephone instrument. comprising fixed windings and a diaphraginof conduct-- ing material adjacent thereto, said windings being adapted to carry a direct current whereby a radial magnetic field may be produced throughout substantially the entire area of the diaphragm, and to carry a variable current which will induce corresponding variable currents in said diaphragm and produce vibration of the diaphragin solely by reason of the reaction between the variable currents induced therein and the radial magnetic field about the diaphragm produced by the direct current.

6. A telephone instrument consisting of a pair otlike pancake coils mounted upon opposite sides of an electrically conducting diaphragm, said coils being adapted 'to carry simultaneously a variable current and a direct current, the electrical connections of the coils being such that the effect of the direct current is to} produce a constant radial magnetic field in {the 'diapl'iragm,

while the variable currents' -produce variable magnetic field perpendicular to the diaphragm.

7. A telephone instrument consisting 'of a pair of like pancake coils mounted upon opposite sides of an electrically conducting a direct current; the electrical connection rent may be caused t'o ffi'ow through the two of the coils being such that the direct cur coils in series while'the. variable current may be caused t0 flo\v tli-rough the two coils in parallel whereby the magnetic fields produced; by the direct currents in the two coils oppose each other and the magnetic fields produced by the reliable current in the two coils assist each other and cause variable currents to be-induced in the diaphragm.

8;. A- telephone in'strument consisting of a pair of fixed pancakecoils' mounted'upon opposite sides of a diaphragmdormed;of electrically conducting material, said coils being adapted to carry a direct current pro ducing a ,constant radial magnetic field 111;.- the diaphragm, whereby mechanlc-al vibra-' tion of the diaphragm by soundwaves impinging thereagainst'will result in the gen-.

eration of variablecurrents in the diawhich currents wilt-induce corresponding currents in the pancake COIlS.

a P i of fixed pancake coils mounted upon opposite sides o'i' a diaphragm'formed' of electrically conducting non-magnetic. ma- .terial, said coils'being-adapted to 'carry a directj cui'frent producinga constant radial from one another.

magnetic field in the diaphragm, whereby 'mechanical vibration ofthe diaphragm by sound waves impinging thereagai'nst will result 111 the generation of variable currents;-

in the diaphragm corresponding to the sound waves, which currents will induce corresponding currents in the pancake'coilsa l0. A telephone instrument consisting of a diaphragm of electrical conducting non-' magnetic material, and a pancake coily mounted adjacent to and parallel with said diaphragm and distributed over an area-- substantially equal to that of the diaphragimi I a supporting striicturq qa W' ibratory diaphragm of conducting-'- material" mounted within said support,- {and a pair'of pancake, coils mounted upomjopposite' sides in close parallel relation :to the-diaphragm, said coils being 'a'daptedto carry a-direct current and'a-voic'e current, and formed-of annular' concentric sections spaced apartfho'm one another. v 12..In a' telephone instrument, a supporting structure, a diaphragm of non-magnetic 4 (conducting material mounted therein, and phragm corresponding to the sound waves;

pancake coils mounted at oppositeflsides thereof inclosewparallel relation thereto,

-i.eac h"of said coilsconsisting of a seriesof 9. A telephonemstrument consisting of annular concentric sections spaced apart ture.

CLARENCE WILSON IL TT; 

